Instrument for adjustment osteotomy of a lower extremity

ABSTRACT

An instrument for performing a correctional osteotomy of a lower extremity of a patient has a securing frame (1), fixation elements (7, 8) for attaching the frame to the skeleton of the lower extremity of the patient, and securing components (6, 9) adjustably holding the fixation elements on the frame. A saw guide (25) is mounted on said frame so as to be angularly adjustable relative to the frame. An angle-indicating scale plate (10) is adjustably attached to one of the securing components. A rotation axis pin (12) penetrates the scale plate and points toward a location on the skeleton for intersection of bone cuts to be made. An angle determining component (23) is pivotable about the rotation axis pin and carries the saw guide and two pointers (26, 27) aligned with each other and alignable with a projection of a mechanical loading axis of the extremity of the patient, whereby adjustment of the pointers directly causes adjustment of the saw guide.

This application is filed under 35 USC 371 based on PCT/CH96/00195 filedon May 21, 1996.

FIELD OF THE INVENTION

This invention relates to instruments for the support of an orthopedicsurgical operation for correction of the mechanical loadingcircumstances at the knee wherein a frame is attachable to the skeletonby two fixation elements with a saw guide angularly adjustable relativeto the frame.

BACKGROUND OF THE INVENTION

The specific correction of the mechanical loading circumstances at theknee in a case of one-sided degenerated illness is a known and oftenapplied method to regain freedom from pain and to enhance mobilitywithout providing a prosthesis. In an orthopedic surgical operation, theposition of the axis of the lower extremity is altered so that a reliefof stress on the affected joint segment is achieved. The most commonlyapplied variant of this operation is the lateral set-on valgusatingtibia-head-osteotomy when there is an existing impairment of the medialjoint portion. In this procedure, an alteration of the axis of the legtoward knock knees is produced through removal of a wedge-shaped bonechip producing release of the ill medial joint compartment. Conditionsfor the clinical success of the adjustment osteotomy are, apart from thecorrect indication position, the exact determination of the correctingangle, the removal of a wedge-shaped bone chip corresponding to thecorrection angle, the quality of the areas of osteotomy and the stablemicro-motion-free osteosynthesis by means of a suitable osteosynthesisimplant.

In the case of a medial gonarthrosis, the mechanical axis that forms astraight line through the joint centers of the hip, knee and anklejoints in a healthy knee is displaced through the rearrangement by 20 to30 mm toward the lateral joint part. The correction angle is the sum ofthe existing false position and an over-correction of the mechanicalaxis. Because of that over-correction, the load on the ill joint half isreduced and the opposite, healthy half is loaded a little more strongly.The bone wedge which is to be removed can either be removedhorizontally, i.e., perpendicular to the axis of the diaphysis, or at anangle to it. When using the mentioned instruments, we choose anosteotomy course which is inclined rising toward the ill side todetermine the rotating point of the osteotomy in the compact subchondralbone a few millimeters from the lateral limiting corticalis. The bonebridge so attained produces a tension boom and allows the simpleosteosynthesis of the osteotomy by means of a reciprocal attachedimplant. For the production of this bone bridge, which is important forstability, the final choice of the general osteotomy angle relative tothe joint axis is important since the crossing point of the wedge-shapedosteotomy in the compact bone volume directly below the joint providesgood conditions for undisturbed healing without secondary correctionloss.

For planning the operation, one uses an x-ray photograph of the fulllength of the extremity, centered on the joint, with the plane of thephotograph corresponding with the frontal plane as exactly as possibleto avoid projection errors. When taking measurements from the x-rayphotograph, the factor of enlargement must be considered. Because x-rayphotographs are affected by a nonlinear enlargement factor going outfrom the center of the ray, and the plane of the photography lies as arule not exactly in the axis of the body because of positioninaccuracies, this planning is always affected with faults. Withpatients of advanced age, the photography technique is often especiallydifficult. With given contraction of flexion, minor differences ofrotation from the frontal plane have such consequences that the accuracywhich is necessary to reach an optimal result is not given in planning.For conversion of the correction angle from the planning todetermination of the guidance of the sawing tool angle, it is customaryto use instruments which are attached to the skeleton and are providedwith arrangements for guidance of a mechanically driven saw blade.

The authors of EP application 0 231 885 suggest the attachment of aninstrument shaped as a circular arc and scaled in angular degrees bymeans of two pins which are positioned above and below the osteotomy inthe tibia. The pins are positioned relative to each other along linesrepresenting the wedge angle of the osteotomy. These pins carry a platewhich forms the guide for the saw when positioned against the bone. Withthis, the angle and the plane of the wedge-shaped converging osteotomyplanes are determined. Not determined is the location of the coincidenceof the saw cuts at the peak of the bone wedge which is to be removed.This should, in the ideal case, be set some millimeters before theopposite cortical shell in the compact joint close spongiosa of thetibia so that, on one side, the osteotomy areas are apt to fit over thewhole cross-section of the bone and on the other side, a minimal bonevolume connected with shortening of the leg is removed, as little as ispossible. Preservation of a thin deformable bone bridge is desired andensures certain allocation of the osteotomy segments and increases thestability of the subsequent osteosynthesis in the sense of a tensionboom. With the instrument suggested in EP 0 231 885, this crossinglocation is to be determined from the x-ray photograph and theinstrument must be installed during the operation at the tibia withdistance and orientation according to the planning. In this realization,the location of the cut edge is the central point of theangle-determining circular arc segment of the instrument.

In French patent application 2,679,126, a similar arrangement isdescribed which is likewise attached to the skeleton by pins and allowsosteotomies which permit the removal of a bone wedge sequently with asaw guide including a guide rail in the shape of a circular arc segmentwhich exactly guides the saw, the saw being a reciprocating bone sawpivotable in angular degrees. In this device, the crossing location ofthe saw cuts must be planned on an x-ray photograph and transferred tothe situation during the operation.

As described above, planning using an x-ray photograph contains someinevitable inaccuracies. In addition, it is to be expected that, whenpositioning one of the above described instruments on the patient,further inaccuracies will appear as to the location of the osteotomywedge, particularly as the result of the fact that the positioning isnot directly examinable in advance.

SUMMARY OF THE INVENTION

An object of the invention is to provide an instrument which allows oneto perform adjusting wedge-shaped osteotomies on a lower extremity withhigh accuracy in which the result is independent of inaccuraciesassociated with planning using x-ray photographs. Additionally, thepaths of the bone cuts, and particularly their intersection or crossinglocation, is to be exactly determinable and examinable before theirexecution.

An instrument in accordance with the invention has a securing frameenclosing the extremity which is attached to the skeleton of the patientsurrounding the bone areas to be cut and which is a reference for theangle determining part. For fixating the securing frame, the subsequentanchorage of the implant used for the osteosynthesis and one or morepins to be bored into the bone are used. The securing frame forms thebasis for a system of coordinates for the position and the correctionangle of the correction osteotomy. On the angle determining part isguided the saw guide and a pointer system connected with it andrepresenting the projection of the mechanical proportion of the axis.Alteration of the mechanical axis indicated by pivoting the pointers isconsequently directly transferred to the saw guide. The rotation axis ofthe angle determining part corresponds to the crossing location of thebone cuts executed along the saw guide. By means of the guide andclamping devices, the rotation axis is freely selectable and is directlyindicated at the skeleton. Thus, all of the variables determining theoperation are adjustable directly at the skeleton and are examinable,and are therefore independent of planning, affected by mistakes on thebasis of x-ray photographs.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention for a valgusatedtibia-correction-osteotomy is described in the following with referenceto the accompanying drawings, wherein:

FIG. 1 is a schematic front elevation of a skeletal lower extremity of apatient with an instrument according to the invention positionedthereon; and

FIG. 2 is an enlarged partial schematic diagram of a portion of theapparatus of FIG. 1 showing wedge-shaped saw cuts of the correctionosteotomy with a predetermined crossing location of the cuts.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A securing frame 1 is fixed to the skeleton on both sides below theknee. Parallel legs 2 and 3 of the securing frame are connectedrespectively by a pin guide 6 and a securing clamp 9 at least one ofwhich is attached so that it is pivotable about an axis or moveable in aplane. In the example shown, clamp 9 is pivotably attached and isclampable around the axis of leg 3 of the securing frame. About 6 to 10mm below the joint plane, a pin 7 guided in pin guide 6 is insertedparallel to the joint plane from the medial into the bone so that theposition of the pin is adjustable along the pin guide and perpendicularto it by a clamp guide 4.

A bone chisel 8 which is held in clamp 9 and driven into the bone formsthe lateral attachment. In order to use the instrument at the leftrather than the right extremity, the clamping of bone chisel 8 and theguide rail for pin guide 6 are mounted in a position reversed 180° fromthat shown. The two attachment elements, pin 7 and bone chisel 8, areadjustable in height so that the securing frame is positionable relativeto the skeleton. Bone chisel 8 may additionally serve for fixation ofthe instrument for preparation of the bone bearing for the subsequentosteosynthesis implant, for example, a bent half-tube plate. On pinguide 6, an angle determining part 10 is movably attached so that thecenter of rotation 11 of the angle determining part represents acrossing point 21 of bone cuts 20. This point is indicated by alowerable pin 12 penetrating part 10 and pointing directly at theskeleton.

The general angle of the wedge-shaped osteotomy to the tibial axis maybe chosen freely through the initial angle of a pivoting arm 23. On thepivoting arm, which is shaped as a longitudinal guide, a saw guide 25and a pointer holding device 24, which is pivotable and clampable initself, is guided.

Small medial and enlarged lateral incisions are made and the instrumentis then attached to the skeleton, after which the crossing point of thesaw cuts is set by moving angle determining part 10. After the choice ofthe general angle of the osteotomy is made, the pair of pointerscomprising hip side pointer 26 and tibia side pointer 27 is positionedabove the center of the knee, adjusted parallel with the tibial axis 22and clamped relative to pivoting arm 23 by means of pointer holdingdevice 24. The angular position of the pivoting arm may be read on theangle scale and can be determined from the clamping screw at therotation axis. For execution of the first saw cut, saw guide 25 ispushed against the bone, clamped at the pivoting arm and secured in thisposition by a pin which is positioned in the bone by a correspondingborehole in the saw guide.

After previous osteotomy of the fibula, the first saw cut of thewedge-shaped osteotomy is made. The pin locking of the saw guide isloosened and the correction of the leg axis is adjusted through thepointer pointing toward the hip joint. The spina iliacaanterior-superior, which is easy to identify during the operation and issituated 2-3 cm lateral of the center of the hip joint, serves as areference. For achievement of the desired over-correction, hip pointer26 is adjusted to a point 4.5 to 7 centimeters medial of the spina. Thisadjustment method, having reference points lying far apart, offers theadvantage of small errors. The easily meetable measuring tolerance ofone centimeter by the adjustment of the pointers relative to the spinaproduces a maximum angular error of approximately 1 to 1.5°. Theaccuracy which is necessary for an optimal result of the operation is 2to 3°, which is far larger than the maximum anticipated error achievablewith an instrument according to the invention.

By adjustment of hip pointer 26, pivoting arm 23 of the instrument andtherewith saw guide 25 are automatically likewise rotated to thecorrection angle. For controlling, the chosen correction angle may beread directly on a scale at angle determining part 10. From thepointers, which represent the mechanical axes of the leg, the correctionmay be effected directly related to the axes. The correction angleresults therefrom and may be read, although knowledge of this angle isnot necessary for completion of the operation. After the chosencorrection has been set, the saw guide is fixed again in the newposition by the pin which passes through the borehole of the saw guide,and the second saw cut is made. After removal of the bone wedge, theinstrument is removed from the skeleton and the osteotomy areas areclosed toward each other. The adapted osteosynthesis implant, a benthalf-tube plate, is anchored in a bearing prepared by bone chisel 8 andscrewed down against the tibia. Alternatively, other implants may beused, for instance bone clamps.

I claim:
 1. An instrument for performing an adjustment osteotomy of alower extremity of a patient comprisinga securing frame (1); first andsecond fixation elements (7, 8) for attaching said frame to the skeletonof a lower extremity of a patient; first and second securing components(6, 9) adjustably holding said first and second fixation elements,respectively, on said frame; a saw guide (25) mounted on said frame,said saw guide being adjustable to a plurality of angles relative tosaid frame; an angle-indicating scale plate (10) adjustably attached toone of said securing components; a rotation axis pin (12) penetratingsaid scale plate for pointing toward a location on said skeleton forintersection of bone cuts to be made therein; and an angle determiningcomponent (23) pivotable about said rotation axis pin and carrying saidsaw guide and two pointers (26, 27) aligned with each other andalignable with a projection of a mechanical loading axis of theextremity of the patient, whereby adjustment of said pointers directlycauses adjustment of said saw guide.
 2. An instrument according to claim1 wherein said frame is generally C-shaped comprising two parallel legs,one of said securing components being attached to each of said parallellegs.
 3. An instrument according to claim 2 wherein at least one of saidsecuring components (6, 9) is adjustable relative to said parallel leg.4. An instrument according to claim 1 wherein said first fixationelement comprises a pin (7), said first securing component (6) comprisesa pin guide with a guide clamp holding said pin so that the height ofsaid pin relative to said frame is adjustable.
 5. An instrumentaccording to claim 4 wherein said second fixation element comprises abone chisel (8) and said second securing component (9) comprises achisel clamp holding said chisel, said chisel clamp being pivotablerelative to said frame.
 6. An instrument according to claim 1 includinga fastening element (24) connecting said two pointers (26, 27) to saidsaw guide, said fastening element permitting angular adjustment of saidpointers relative to said saw guide.
 7. An instrument according to claim1 wherein the length of each of said two pointers (26, 27) isadjustable.
 8. An instrument according to claim 7 wherein each of saidtwo pointers comprises telescoping sections permitting said length to beadjustable.